Mesoporous sieves having mean pores sizes in the range 2 nm≦Dp≦50 nm are potentially useful materials for applications as catalysts components in the oil refining, petrochemical and chemical industries, mainly due to their wide open structure and intrinsic surface acidity. Mesoporous silica and silica-alumina based materials have been developed recently and tested for the selective separation of components in water-hydrocarbons and hydrocarbons mixtures. Other synthetic large sorption capacity silica and silica-alumina based materials having uniformly sized large pores arranged hexagonally have selective properties for benzene adsorption of up to 15 g/100 g at 50 torr and at 25° C. These materials are also suitable for the catalytic de-alkylation of tri-tert-butylbenzene (TTB) to di-tert-butylbenzene at 225° C. WHSV=100 h−1 or at 200° C. and 200 h−1.
Other synthetic materials have been synthesized using surfactants in aqueous solutions, such as for example cetyltrimethylammonium bromide (CTAB) and poly(alkylene oxide) block copolymers. The typical pore array symmetries of these materials are hexagonal, cubic or lamellar, which correspond to MCM-41, MCM-48 and MCM-50 type structures, respectively. Other mesoporous sieves having larger pore diameters have been synthesized under acidic or neutral conditions, giving rise to SBA-15, MSU-H, Al-MSU-S or “wormhole-like” structures.
Micron- and sub-micron sized silica spheres with an amorphous inner structure were previously synthesized. When an organic surfactant is introduced, sub-micrometer sized particles having characteristics of the MCM-41 materials have been obtained. These materials have been used as GC stationary phases. Recently, TEM techniques were applied for verifying the formation of spherical MCM-41 particles of 0.2 to 1.0μ diameter having an ill-ordered hexagonal structure and a spherical distribution of pores with an hexagonal packing on a local scale. When octylamine is introduced in the batch synthesis a disordered “wormhole-like” pore structure forms into the large 30 to 50μ diameter silica hard spheres.
Other developments have led to synthesis of spherical MCM-48 type materials from novel routes based on the modified Stöber modified method used for obtaining non-porous silica. These developments have led to catalysts composed of discrete silica and silica-metal oxide particles containing aluminum, gallium, niobium, vanadium or chromium, the latter also being used for the polymerization of low molecular weight olefins. Other mesoporous silica based materials prepared by the cationic polymer dispersion in water reaction medium or using sol-gel methods have surface areas of about 500 m2/g. However, in these cases no specific details were disclosed on the particle morphology or their inner pore structure.
One example of a catalyst comprising discrete silica particles is disclosed in U.S. Pat. No. 5,670,438 to Bradley. The catalyst composition is produced by contacting a catalyst support with a colloidal suspension of a tetraalkyloxysilane, an alcoholic composition, an ammonia composition and water. The catalyst support contains a chromium compound.
U.S. Pat. No. 5,951,962 to Muller et al. discloses a mesoporous silica having a specific surface area of 500 m2/g and a volume of the mesopores of 1.0 ml/g. The mesoporous silica is produced by converting a silica precursor in the presence of a polymer dispersion. The resulting silica particles have pores with an average pore diameter of 2–50 nm.
U.S. Pat. No. 5,712,037 to Anderson et al. discloses a method of producing a high surface area microporous ceramic material by replacing a portion of the silicon in a sol or gel that contains silica with cations of a metal. The substituted sol or gel is then converted into a porous ceramic material by evaporating the solvent and calcining the support. The microporous materials have a mean pore diameter of less than 20 angstroms.
U.S. Pat. No. 5,098,684 to Kresge et al. discloses an ultra-large pore crystalline material having a hexagonal arrangement of uniformly-sized pores. The pores are disclosed as having a diameter of at least 15 angstroms.
The prior porous particles and process for producing the particles have been generally effective for the intended use. However, there is a continuing need in the industry for improved porous materials and methods of producing the materials.